docs: def with_upcoming_occurrences(self):
          """
          :return: events having upcoming occurrences, and all their children
          """
          return self.filter(
              Q(is_drop_in=False, occurrences__start__gte=djtz.now) |
              Q(Q(is_drop_in=True) | Q(occurrences__is_all_day=True), occurrences__end__gt=djtz.now)
          )